If you put 100 children on growth hormone for idiopathic isolated growth hormone deficiency and then retest them years later, how many still meet the diagnostic criteria they started on? A systematic review published this year in the Journal of the Endocrine Society pooled 31 studies and 2,057 patients to answer that. At retesting near adult height, the mean reversal rate was 69.6% — meaning roughly seven in ten no longer tested as deficient.

That is not a fringe claim about a research peptide. Somatropin is one of the most established prescription hormones in endocrinology, TGA-approved and PBS-subsidised in Australia for defined conditions. What the retesting literature exposes is something narrower and more uncomfortable: the test used to open the door is noisier than the treatment behind it. If you are researching HGH and want to understand why "growth hormone deficiency" is not a fixed label, this is the paper to know about.

What is HGH, and what is actually being diagnosed?

Human growth hormone (somatropin) is recombinant human GH, a 191-amino-acid protein identical to the pituitary hormone. In children it drives linear growth; in adults it influences body composition, bone turnover and lipid handling. Our fuller background sits on the HGH profile page.

Crucially, there is no simple blood test for deficiency. GH is secreted in pulses, so a random level says little. Diagnosis relies on GH stimulation tests — insulin, glucagon, arginine, clonidine or GHRH-arginine — where a drug provokes the pituitary and peak GH is measured against a threshold. As the Endotext review of adult stimulation testing puts it plainly, these tests are not physiological, the cut-off is arbitrary, reproducibility is uncertain, and inter-test variability is high.

That is the foundation the whole diagnostic edifice rests on.

The 2026 systematic review: three retest windows, three reversal rates

The review searched four databases to June 2025 and included studies that retested children originally diagnosed with idiopathic isolated GH deficiency — the largest and most ambiguous diagnostic category, where no structural pituitary lesion, genetic cause or additional hormone deficit explains the result.

Mean reversal rates by retesting timing:

  • After 1–2 years of rhGH treatment: 46.4%
  • During mid-puberty: 46.3%
  • At or near adult height: 69.6%

Read carefully: these are means across different studies with different protocols, not one cohort followed through three checkpoints. The review's own conclusion is that protocols need standardising and that long-term outcome studies are needed "to optimise care and reduce overtreatment."

Why the number climbs — and why that is not one single story

Several explanations sit on top of each other, and the review does not fully separate them.

Genuine transience. Some children have a real but temporary shortfall in GH secretion that resolves as the hypothalamic-pituitary axis matures. That is a biological reversal, not a diagnostic error.

Pubertal physiology. GH secretion rises sharply during puberty under sex-steroid drive. A prepubertal child tested without priming can fail a threshold that the same child clears comfortably two years later. The review notes that priming with sex steroids was applied inconsistently across studies — testosterone in boys, ethinyl estradiol in girls — which alone could shift reversal rates.

Test noise. Given the documented inter-test variability, a proportion of both original diagnoses and subsequent "normal" retests are simply measurement scatter around an arbitrary line.

You cannot tell from a pooled reversal rate which of these dominates. Anyone quoting "70% were misdiagnosed" is over-reading the paper.

The BMI problem layered on top

A separate 2026 retrospective analysis in Children looked at how body weight distorts stimulation testing in paediatric assessment. Overweight and obese children showed false-positive clonidine stimulation test results at 25.5%, versus 9.3% in non-obese children — elevated BMI cut both specificity and overall accuracy.

The mechanism is well described in older work: higher BMI suppresses stimulated GH peaks, so a heavier child can fail a test on adiposity rather than pituitary function. The same logic applies in adults, where reviewers have argued for lowering the adult cut-point from 3 µg/L toward 1 µg/L in obese patients to avoid misclassification.

Both findings are retrospective and single-context. They are consistent with a large prior literature rather than novel, but neither has been settled by a prospective trial.

Is HGH legal in Australia, and how do the PBS criteria handle this?

Here is the genuine HGH Australia angle, and it is more interesting than the usual regulatory recap.

Somatropin is Schedule 4 (prescription only) and border-controlled — importing or possessing it without a prescription is illegal, regardless of how it is marketed online. It is TGA-registered and PBS-subsidised for specific indications, with growth hormone listed for adults with severe deficiency since December 2018.

Australia's subsidy criteria are deliberately strict, and they are strict precisely because the test is unreliable. Per the Australian endocrinology guidance, adult PBS eligibility requires a documented stimulation test result such as an insulin tolerance test with peak GH below 2.5 µg/L, an arginine infusion below 0.4 µg/L, or glucagon provocation below 3 µg/L. That ITT threshold is well under the 5.1 µg/L cut-off at which the test performs best diagnostically — Australia has traded sensitivity for specificity to restrict subsidy to unambiguous cases.

And on the paediatric-to-adult transition, Hormones Australia's patient guidance is explicit: adults previously diagnosed with childhood-onset GH deficiency should be retested at the end of adolescence to assess whether the condition persists. Treatment is not assumed to be lifelong. The systematic review is, in effect, quantifying why that recommendation exists.

Paediatric and adult PBS access in Australia runs through authority applications and specialist programs with defined criteria — it is not a matter of asking for a script. We cover Australian access pathways across the peptides library.

What this does and doesn't say about HGH for anti-ageing

None of the above should be read as encouragement. The retesting literature is about people who may not need somatropin. It says nothing favourable about healthy adults taking it.

On that question the evidence has been stable for years: trials in healthy older adults show roughly 2 kg of lean mass gain, without convincing gains in strength or function, and with real side effects — oedema, joint pain, carpal tunnel symptoms and worsened insulin resistance. Somatropin is also prohibited at all times by WADA, in and out of competition.

The honest summary: somatropin is a well-evidenced replacement therapy for a condition that is genuinely hard to diagnose, and a poor bet as an enhancement drug.

What to watch

Three things would move this field:

  1. Protocol standardisation. Until priming, assay and cut-off practice are harmonised, reversal rates will keep varying by centre rather than by biology.
  2. Long-term outcomes in reversers. What happens to body composition, bone density and metabolic markers in people who stop after a normal retest? The review flags this as unanswered.
  3. Two-step diagnostics. Combining IGF-1 and growth velocity with stimulation testing has been proposed to separate true deficiency from obesity-related GH suppression. That needs prospective validation, not more retrospective series.

Want the evidence, not the marketing? Join the free updates list for measured coverage of peptide and metabolic research from an Australian perspective.

FAQ

What is HGH used for?

Somatropin is TGA-approved and PBS-subsidised in Australia for defined conditions including paediatric growth hormone deficiency, severe adult growth hormone deficiency, Turner syndrome and several other specific diagnoses. It is not approved for anti-ageing, bodybuilding or general wellbeing.

Is HGH legal in Australia?

Somatropin is a Schedule 4 prescription-only medicine and is border-controlled, so possessing or importing it without a valid prescription is illegal. It is also prohibited at all times by WADA for athletes.

Can growth hormone deficiency go away?

Yes — in the idiopathic isolated form it often does. A 2026 systematic review of 31 studies and 2,057 patients found mean reversal rates on retesting of 46.4% after 1–2 years of treatment, 46.3% at mid-puberty and 69.6% at or near adult height.

Does HGH work for anti-ageing?

The trial evidence in healthy older adults shows roughly 2 kg of lean mass gain without reliable improvements in strength or function, alongside oedema, joint pain and worsened insulin resistance. It is not an approved or evidence-supported anti-ageing use.

Sources

This article is information only, not medical advice. Somatropin (HGH) is TGA-approved and PBS-subsidised in Australia for defined conditions, is Schedule 4 prescription-only and border-controlled, and is WADA-prohibited; retatrutide.net.au is independent and does not sell or source any compound.